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come to be a more or less hereditary habit, though the original 

 causes still undoubtedly exert a very strong influence. Dr. C. Hart 

 Merriam,* in treating of the subject, gives the following as the most 

 potent causes of the spring migration of birds: 1. The food supply 

 fails. 2. The climatic conditions become unsuited to their needs. 

 3. The approach of the breeding season gives rise to physiological 

 restlessness. 4. The birds inherit an irresistible impulse to move at 

 this particular time of year. 



The fall migration is evidently due to similar causes, with the ex- 

 ception, of course, of tiie third. 



Birds may be arranged in two groups, according to their manner 

 of migration, viz.: day migrants and night migrants. The former 

 include the Doves, Hawks, Hummingbirds, Chimney Swift, Night- 

 hawk, Horned Lark, Crows, Jays, Grackles, Blackbirds, Swallows, 

 Cedarbird, Tit Lark, Bluebird and Robin, and perhaps a few others. 



The niglit migrants include the Woodpeckers, Cuckoos, Fly- 

 catchers (except the Kingbird), Meadowlark, Orioles, most of the 

 Finches, the Vireos, Tanagers, Warblers, Wrens, Creepers, Nut- 

 hatches, Titmice and most of the Thrushes. 



Among the water birds, the Bittern, Woodcock, Wilson's Snipe, 

 Spotted Sandpiper and the Rails migrate exclusively by night, while 

 the other species seem to move by day or night, according to circum- 

 stances, most diving birds migrating along the coasts by day but 

 making their overland journeys by night.f 



From an examination of the foregoing lists it will be seen that the 

 more timid, shelter-loving birds migrate at night, and the bolder spe- 

 cies, which are strong of flight or which associate in flocks, migrate 

 by day. The reasons for this can easily be seen in the following 

 quotation from Mr. Brewster's paper on Bird Migration : " Timid, 

 sedentary, or feeble-winged birds migrate by night because they are 

 either afraid to venture on long, exposed journeys by daylight, or 

 unable to continue these journeys day after day without losing much 

 time in stopping to search for food. By taking the nights for trav- 

 eling they can devote the days entirely to feeding and resting in 

 their favorite haunts. Good examples are Thrushes (except the 

 Robin), Wrens, Warblers and Vireos. Bold, restless, strong-winged 

 birds migrate chiefly, or very freely, by day because, being accus- 

 tomed to seek their food in open situations, they are indifferent to 

 concealment, and being further able to accomplish long distances rap- 



*Bird Migration in the Mississippi Valley, p. 1, footnote. f Brewster. 



